Terminal apparatus and method for transmitting a response signal at a terminal

ABSTRACT

A radio communication mobile station device reduces the number of blind decoding processes at a mobile station without increasing overhead by report information. The device includes a judgment unit which judges a particular PUCCH to which a response signal corresponding to the downstream line data is to be allocated among a plurality of PUCCH, according to a CCE occupied by PDCCH allocated to a particular search space corresponding to a CCE aggregation size or the PDCCH to which allocation information destined to the local station is allocated among search spaces changing in accordance with the CFI value; and a control unit which controls a cyclic shift amount of a ZAC sequence of the response signal and a block-wise spread code sequence according to a correspondence between CCE occupied by PDCCH allocated to a particular search space and a particular PUCCH resource, the correspondence changing in accordance with the CFI value.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of application Ser. No. 12/739,687filed Apr. 23, 2010, which is a 371 application of PCT/JP2008/003070filed Oct. 28, 2008, which is based on Japanese Application No.2007-280,921 filed Oct. 29, 2007, the entire contents of each of whichare incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a radio communication mobile stationapparatus and response signal spreading sequence control method.

BACKGROUND ART

In mobile communication, ARQ (Automatic Repeat reQuest) is applied todownlink data from a radio communication base station apparatus(hereinafter abbreviated to “base station”) to radio communicationmobile station apparatuses (hereinafter abbreviated to “mobilestations”). That is, mobile stations feed back response signalsrepresenting error detection results of downlink data, to the basestation. Mobile stations perform a CRC (Cyclic Redundancy Check)detection of downlink data, and, if CRC=OK is found (i.e. if no error isfound), feed back an ACK (ACKnowledgement), or, if CRC=NG is found (i.e.if error is found), feed back a NACK (Negative ACKnowledgement), as aresponse signal to the base station. These response signals aretransmitted to the base station using uplink control channels such asPUCCH's (Physical Uplink Control CHannels).

Also, the base station transmits control information for notifyingresource allocation results for downlink data and uplink data, to mobilestations. This control information is transmitted to the mobile stationsusing downlink control channels such as PDCCH's (Physical DownlinkControl CHannels). Each PDCCH occupies one or a plurality of CCE's(Control Channel Elements). The base station generates PDCCH's permobile station, allocates CCE's to be occupied by the PDCCH's accordingto the number of CCE's required for control information, maps thecontrol information on the physical resources associated with theallocated CCE's, and transmits the results.

For example, in order to satisfy desired received quality, an MCS(Modulation and Coding Scheme) of a low MCS level needs to be set for amobile station that is located near the cell boundary where channelquality is poor. Therefore, the base station transmits a PDCCH thatoccupies a larger number of CCE's (e.g. eight CCE's). By contrast, evenif the MSC of a high MCS level is set for a mobile station that islocated near the center of a cell where channel quality is good, it ispossible to satisfy desired received quality. Therefore, the basestation transmits a PDCCH that occupies a smaller number of CCE's (e.g.one CCE). Here, the number of CCE's occupied by one PDCCH is referred toas “CCE aggregation size.”

Also, a base station allocates a plurality of mobile stations to onesubframe and therefore transmits a plurality of PDCCH's at the sametime. In this case, the base station transmits control informationincluding CRC bits scrambled by the mobile station ID numbers of thedestination, so that the destination mobile station of each PDCCH can beidentified. Further, the mobile stations decode CCE's to which PDCCH'smay be mapped, and perform CRC detection after descrambling, the CRCbits by the mobile station ID numbers of those mobile stations. Thus,mobile stations detect the PDCCH's for those mobile stations byperforming blind decoding of a plurality of PDCCH's included in areceived signal.

However, if a larger total number of CCE's are present, the number oftimes a mobile station performs blind decoding increases. Therefore, forthe purpose of reducing the number of times a mobile station performsblind decoding, a method of limiting CCE's targeted for blind decodingon a per mobile station basis is studied (see Non-Patent Document 1).With this method, a plurality of mobile stations are grouped, and CCEfields being CCE's targeted for blind decoding are limited on a pergroup basis. By this means, the mobile station of each group needs toperform blind decoding of only the CCE field allocated to that mobilestation, so that it is possible to reduce the number of times of blinddecoding. Here, the CCE field targeted for blind decoding by a mobilestation is referred to as “search space.”

Also, to use downlink communication resources efficiently withoutsignaling to notify PUCCH's for transmitting response signals, from thebase station to the mobile stations for transmitting response signals,studies are underway to associate CCE's and PUCCH's on a one-to-onebasis (see Non-Patent Document 2). According to this association, eachmobile station can decide the PUCCH to use to transmit a response signalfrom that mobile station, from the CCE associated with the physicalresource on which control information for that mobile station is mapped.Therefore, each mobile station maps a response signal from that mobilestation on a physical resource, based on the CCE associated with thephysical resource on which control information for that mobile stationis mapped.

-   Non-Patent Document 1: 3GPP RAN WG1 Meeting document, R1-073996,    “Search Space definition: Reduced PDCCH blind detection for split    PDCCH search space”, Motorola-   Non-Patent Document 1: 3GPP RAN WG1 Meeting document, R1-073620,    “Clarification of Implicit Resource Allocation of Uplink ACK/NACK    Signal”, Panasonic

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, if a plurality of mobile stations are grouped and search spacesare set on a per group basis, a base station needs to notify searchspace information indicating the search space of each mobile station, toeach mobile station. Therefore, in the above conventional technique, theoverhead increases due to notification information.

It is therefore an object of the present invention to provide a radiocommunication mobile station apparatus and response signal spreadingsequence control method for reducing the number of times a mobilestation performs blind decoding, without increasing the overhead bynotification information.

Means for Solving the Problem

The radio communication mobile station apparatus employs a configurationhaving: a receiving section that receives a first control channel whichoccupies one or a plurality of control channel elements and which isallocated to a specific control channel element field matching a numberof control channel elements occupied by the first control channel, amonga plurality of control channel element fields that vary depending on acontrol format indicator value; a deciding section that decides aspecific second control channel to which a response signal to downlinkdata is allocated among a plurality of second control channels, based onthe control channel element occupied by the first control channel; and acontrol section that controls a spreading sequence for the responsesignal, according to an association which associates the control channelelement occupied by the first control channel and a spreading sequenceof the specific second control channel and which varies depending on thecontrol format indicator value.

Advantageous Effect of the Invention

According to the present invention, it is possible to reduce the numberof times a mobile station performs blind decoding, without increasingthe overhead due to notification information.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the configuration of a base stationaccording to Embodiment 1 of the present invention;

FIG. 2 is a block diagram showing the configuration of a mobile stationaccording to Embodiment 1 of the present invention;

FIG. 3 shows search space information according to Embodiment 1 of thepresent invention;

FIG. 4 shows search spaces according to Embodiment 1 of the presentinvention;

FIG. 5 shows an example of CCE allocation according to Embodiment 1 ofthe present invention;

FIG. 6 shows search space information according to Embodiment 1 of thepresent invention (in the case where the cell size is large);

FIG. 7 shows search spaces according to Embodiment 1 of the presentinvention (in the case where the cell size is large);

FIG. 8 shows search spaces according to Embodiment 2 of the presentinvention;

FIG. 9 shows search spaces according to Embodiment 3 of the presentinvention (in allocating method 1);

FIG. 10 shows search spaces according to Embodiment 3 of the presentinvention (in allocating method 2);

FIG. 11 shows search spaces according to Embodiment 4 of the presentinvention (CFI=3);

FIG. 12 shows search spaces according to Embodiment 4 of the presentinvention (CFI=2);

FIG. 13 shows search spaces according to Embodiment 4 of the presentinvention (CFI=1);

FIG. 14 shows the priority order relating to a use of physical resourcesassociated with PUCCH's according to Embodiment 5 of the presentinvention;

FIG. 15 shows PUCCH resources according to Embodiment 5 of the presentinvention (CFI=3);

FIG. 16 shows PUCCH resources according to Embodiment 5 of the presentinvention (CFI=2);

FIG. 17 shows PUCCH resources according to Embodiment 5 of the presentinvention (CFI=1);

FIG. 18 shows other search spaces (example 1); and

FIG. 19 shows other search spaces (FIG. 2).

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be explained below in detailwith reference to the accompanying drawings. In the followingexplanation, assume that the total number of CCE's allocated to a PDCCHis 32, from CCE #0 to CCE #31, and the PDCCH CCE aggregation size is oneof 1, 2, 4 and 8. Also, if one PDCCH occupies a plurality of CCE's, theplurality of CCE's occupied by the PDCCH are consecutive.

Also, a case will be explained with the following explanation, where ZAC(Zero Auto Correlation) sequences are used in the first spreading ofPUCCH's and block-wise spreading code sequences, which are used inspreading in LB (Long Block) units, are used in second spreading.However, in the first spreading, it is equally possible to use sequencesthat can be separated from each other by different cyclic shift values,other than ZAC sequences. For example, in the first spreading, it isequally possible to use GCL (Generalized Chirp Like) sequences, CAZAC(Constant Amplitude Zero Auto Correlation) sequences. ZC (Zadoff-Chu)sequences, or use PN sequences such as M sequences and orthogonal Goldcode sequences. Also, in second spreading, as block-wise spreading codesequences, it is possible to use any sequences that can be regarded asorthogonal sequences or substantially orthogonal sequences. For example,in second spreading, it is possible to use Walsh sequences or Fouriersequences as block-wise spreading code sequences.

Also, in the following explanation, assume that the CCE numbers and thePUCCH numbers are associated. That is, the PUCCH number is derived fromthe CCE number used for a PDCCH to use to allocate uplink data.

Embodiment 1

FIG. 1 shows the configuration of base station 100 according to thepresent embodiment, and FIG. 2 shows the configuration of mobile station200 according to the present embodiment.

Here, to avoid complicated explanation, FIG. 1 shows componentsassociated with transmission of downlink data and components associatedwith reception of uplink response signals to downlink data, which areclosely related to the present invention, and the illustration andexplanation of the components associated with reception of uplink datawill be omitted. Similarly, FIG. 2 shows components associated withreception of downlink data and components associated with transmissionof uplink response signals to downlink data, which are closely relatedto the present invention, and the illustration and explanation of thecomponents associated with transmission of uplink data will be omitted.

In base station 100 shown in FIG. 1, encoding section 101 receives asinput search space information indicating the definition of a searchspace determined by, for example, the cell size and base stationenvironment. Further, encoding section 101 encodes the search spaceinformation received as input, and outputs the result to modulatingsection 102. Next, modulating section 102 modulates the encoded searchspace information received as input from encoding section 101, andoutputs the result to mapping section 108.

Encoding and modulating sections 103-1 to 103-K receive as inputresource allocation information for uplink data or downlink datadirected to mobile stations. Here, each allocation information isallocated to a PDCCH of the CCE aggregation size required to transmitthat allocation information. Further, encoding and modulating sections103-1 to 103-K are provided in association with maximum K mobilestations #1 to #K. In encoding and modulating sections 103-1 to 103-K,encoding sections 11 each encode allocation information received asinput and allocated to PDCCH's, and output the results to modulatingsections 12. Next, modulating sections 12 each modulate the encodedallocation information received as input from encoding sections 11, andoutput the results to CCE allocating section 104.

CCE allocating section 104 allocates the allocation information receivedas input from modulating sections 103-1 to 103-K, to one or a pluralityof CCE's based on search space information. To be more specific, CCEallocating section 104 allocates a PDCCH to a specific search spaceassociated with the CCE aggregation size of that PDCCH, among aplurality of search spaces. Further, CCE allocating section 104 outputsallocation information allocated to CCE's, to mapping section 108. Here,the CCE allocating method in CCE allocating section 104 will bedescribed later.

On the other hand, encoding section 105 encodes transmission data (i.e.downlink data) received as input and outputs the result toretransmission control section 106. Here, if there are a plurality itemsof transmission data for a plurality of mobile stations, encodingsection 105 encodes each of the plurality items of transmission data forthese mobile stations.

Upon the initial transmission, retransmission control section 106 holdsand outputs encoded transmission data of each mobile station tomodulating section 107. Here, retransmission control section 106 holdstransmission data until an ACK from each mobile station is received asinput from deciding section 117. Further, if a NACK from each mobilestation is received as input from deciding section 117, that is, uponretransmission, retransmission control section 106 outputs transmissiondata associated with that NACK to modulating section 107.

Modulating section 107 modulates encoded transmission data received asinput from retransmission control section 106, and outputs the result tomapping section 108.

Mapping section 108 maps allocation information to downlink allocationresources associated with the allocated CCE's among downlink resourcesreserved for PDCCH's, maps search space information to downlinkresources reserved for broadcast channels, and maps transmission data todownlink resources reserved for transmission data. Further, mappingsection 108 outputs signals to which those channels are mapped, to IFFT(Inverse Fast Fourier Transform) section 109.

IFFT section 109 generates an OFDM symbol by performing an IFFT of aplurality of subcarriers to which allocation information, search spaceinformation and transmission data are mapped, and outputs the result toCP (Cyclic Prefix) attaching section 110.

CP attaching section 110 attaches the same signal as the signal at thetail end part of the OFDM symbol, to the head of that OFDM symbol, as aCP.

Radio transmitting section 111 performs transmission processing such asD/A conversion, amplification and up-conversion on the OFDM symbol witha CP, and transmits the result from antenna 112 to mobile station 200(in FIG. 2).

On the other hand, radio receiving section 113 receives a SC-FDMA(Single-Carrier Frequency Division Multiple Access) symbol transmittedfrom each mobile station, via antenna 112, and performs receivingprocessing such as down-conversion and A/D conversion on this SC-FDMAsymbol.

CP removing section 114 removes the CP attached to the SC-FDMA symbolsubjected to receiving processing.

Despreading section 115 despreads the response signal by the block-wisespreading code sequence used in second spreading in mobile station 200,and outputs the despread response signal to correlation processingsection 116.

Correlation processing section 116 finds the correlation value betweenthe despread response signal and the ZAC sequence that is used in thefirst spreading in mobile station 200, and outputs the correlation valueto deciding section 117.

Deciding section 117 detects response signals on a per mobile stationbasis, by detecting the correlation peaks in the detection windows on aper mobile station basis. For example, upon detecting the correlationpeak in detection window #0 for mobile station #0, deciding section 117detects the response signal from mobile station #0. Further, decidingsection 117 decides whether the detected response signal is an ACK orNACK, by synchronization detection using the correlation value of areference signal, and outputs the ACK or NACK to retransmission controlsection 106 on a per mobile station basis.

On the other hand, mobile station 200 shown in FIG. 2 receives searchspace information, allocation information and downlink data transmittedfrom base station 100. The methods of receiving these items ofinformation will be explained below.

In mobile station 200 shown in FIG. 2, radio receiving section 202receives an OFDM symbol transmitted from base station 100 (in FIG. 1),via antenna 201, and performs receiving processing such asdown-conversion and A/D conversion on the OFDM symbol.

CP removing section 203 removes the CP attached to the OFDM symbolsubjected to receiving processing.

FFT (Fast Fourier Transform) section 204 acquires allocationinformation, downlink data and broadcast information including searchspace information, which are mapped on a plurality of subcarriers, byperforming an FFT of the OFDM symbol, and outputs the results toseparating section 205.

Separating section 205 separates broadcast information mapped toresources reserved in advance for broadcast channels, from signalsreceived as input from FFT section 204, and outputs the broadcastinformation to broadcast information decoding section 206 andinformation other than the broadcast information to extracting section207.

Broadcast decoding section 206 decodes the broadcast informationreceived as input from separating section 205 to acquire search spaceinformation, and outputs the search space information to extractingsection 207.

Assume that extracting section 207 and decoding section 209 receive inadvance coding rate information indicating the coding rate of allocationinformation, that is, information indicating the PDCCH CCE aggregationsize.

Also, upon receiving allocation information, extracting section 207extracts allocation information from the plurality of subcarriersaccording to the CCE aggregation size and search space informationreceived as input, and outputs the allocation information todemodulating section 208.

Demodulating section 208 demodulates the allocation information andoutputs the result to decoding section 209.

Decoding section 209 decodes the allocation information according to theCCE aggregation size received as input, and outputs the result todeciding section 210.

On the other hand, upon receiving downlink data, extracting section 207extracts downlink data for the subject mobile station from the pluralityof subcarriers, according to the resource allocation result received asinput from deciding section 210, and outputs the downlink data todemodulating section 212. This downlink data is demodulated indemodulating section 212, decoded in decoding section 213 and receivedas input in CRC section 214.

CRC section 214 performs an error detection of the decoded downlink datausing CRC, generates an ACK in the case of CRC=OK (no error) or a NACKin the case of CRC=NG (error present), as a response signal, and outputsthe generated response signal to modulating section 215. Further, in thecase of CRC=OK (no error), CRC section 214 outputs the decoded downlinkdata as received data.

Deciding section 210 performs a blind detection as to whether or not theallocation information received as input from decoding section 209 isdirected to the subject mobile station. To be more specific, against theallocation information received as input from decoding section 209,deciding section 210 performs a blind detection as to whether or not theallocation information is directed to the subject mobile station. Forexample, deciding section 210 decides that, if CRC=OK is found (i.e. noerror is found) as a result of demasking CRC bits by the ID number ofthe subject mobile station, allocation information is directed to thatmobile station. Further, deciding section 210 outputs the allocationinformation directed to the subject mobile station, that is, theresource allocation result of downlink data for that mobile station, toextracting section 207.

Further, deciding section 210 decides a PUCCH that is used to transmit aresponse signal from the subject mobile station, from the CCE numberassociated with a subcarrier to which a PDCCH is mapped, where theallocation information directed to that mobile station is allocated tothat PDCCH. Further, deciding section 210 outputs the decision result(i.e. PUCCH number) to control section 209. For example, if a CCEassociated with a subcarrier to which PDCCH directed to the subjectmobile station is mapped is CCE #0, deciding section 210 decides thatPUCCH #0 associated with CCE #0 is the PUCCH for that mobile station.Also, for example, if CCE's associated with subcarriers to which PDCCHdirected to the subject mobile station is mapped are CCE #0 to CCE #3,deciding section 210 decides that PUCCH #0 associated with CCE #0 of theminimum number among CCE #0 to CCE #3, is the PUCCH for that mobilestation.

Based on the PUCCH number received as input from deciding section 210,control section 211 controls the cyclic shift value of the ZAC sequenceused in the first spreading in spreading section 216 and the block-wisespreading code sequence used in second spreading in spreading section219. For example, control section 211 selects the ZAC sequence of thecyclic shift value associated with the PUCCH number received as inputfrom deciding section 210, among twelve ZAC sequences from ZAC #0 to ZAC#11, and sets the ZAC sequence in spreading section 216, and selects theblock-wise spreading code sequence associated with the PUCCH numberreceived as input from deciding section 210, among three block-wisespreading code sequences from BW #0 to BW #2, and sets the block-wisespreading code sequence in spreading section 219. That is, controlsection 211 selects one of the plurality of resources defined by ZAC #0to ZAC #11 and by BW #0 to BW #2.

Modulating section 215 modulates the response signal received as inputfrom CRC section 214 and outputs the result to spreading section 216.

Spreading section 216 performs first spreading of the response signal bythe ZAC sequence set in control section 211, and outputs the responsesignal subjected to the first spreading to IFFT section 217. That is,spreading section 216 performs first spreading of the response signalusing the ZAC sequence of the cyclic shift value associated with theresource selected in control section 211.

IFFT section 217 performs an IFFT of the response signal subjected tothe first spreading, and outputs the response signal subjected to anIFFT to CP attaching section 218.

CP attaching section 218 attaches the same signal as the tail end partof the response signal subjected to an IFFT, to the head of thatresponse signal as a CP.

Spreading section 219 performs second spreading of the response signalwith a CP by the block-wise spreading code sequence set in controlsection 211, and outputs the response signal subjected to secondspreading to radio transmitting section 220.

Radio transmitting section 220 performs transmission processing such asD/A conversion, amplification and up-conversion on the response signalsubjected to second spreading, and transmits the result from antenna 201to base station 100 (in FIG. 1).

Next, the CCE allocating method in CCE allocating section 104 will beexplained in detail.

CCE allocating section 104 allocates PDCCH's directed to mobilestations, to a search space associated with the CCE aggregation size ofthose PDCCH's to which allocation information for those mobile stationsis allocated, among a plurality of search spaces.

Here, as shown in FIG. 3, CCE allocating section 104 receives as inputsearch space information defining the CCE numbers representing thestarting locations of search spaces and the numbers of CCE'srepresenting the search space lengths, on a per CCE aggregation sizebasis. For example, the search space associated with a CCE aggregationsize of 1 is defined where the CCE number representing the startinglocation is CCE #0 and the number of CCE's is 10. Similarly, the searchspace associated with a CCE aggregation size of 2 is defined where theCCE number representing the starting location is CCE #4 and the numberof CCE's is 12. The same applies to the case where the CCE aggregationsize is 4 or 8.

Therefore, as shown in FIG. 4, a search space formed with ten CCE's fromCCE #0 to CCE #9 is defined when the CCE aggregation size is 1, a searchspace formed with twelve CCE's from CCE #4 to CCE #15 is defined whenthe CCE aggregation size is 2, a search space formed with sixteen CCE'sfrom CCE #8 to CCE #23 is defined when the CCE aggregation size is 3,and a search space formed with sixteen CCE's from CCE #16 to CCE #31 isdefined when the CCE aggregation size is 4.

That is, as shown in FIG. 4, CCE allocating section 104 can allocatemaximum ten PDCCH's of a CCE aggregation size of 1 to the search spaceof CCE #0 to CCE #9. Similarly, CCE allocating section 104 can allocatemaximum six PDCCH's of a CCE aggregation size of 2 to the search spaceof CCE #4 to CCE #15, allocate maximum four PDCCH's of a CCE aggregationsize of 4 to the search space of CCE #8 to CCE #23, and allocate maximumtwo PDCCH's of a CCE aggregation size of 8 to the search space of CCE#16 to CCE #31.

For example, a case will be explained where CCE allocating section 104of base station 100 allocates six PDCCH's of a CCE aggregation size of1, three PDCCH's of a CCE aggregation size of 2, three PDCCH's of a CCEaggregation size of 4 and one PDCCH of a CCE aggregation size of 8.

First, as shown in FIG. 5, CCE allocating section 104 allocates sixPDCCH's (of a CCE aggregation size of 1) to CCE #0 to CCE #5 in thesearch space (CCE #0 to CCE #9) associated with a CCE aggregation sizeof 1 shown in FIG. 4. Next, as shown in FIG. 5, CCE allocating section104 allocates three PDCCH's (of a CCE aggregation size of 2) to CCE's #6and #7, CCE's #8 and #9 and CCE's #10 and #11, to which PDCCH's of a CCEaggregation size of 1 are not allocated, in the search space (CCE #4 toCCE #15) associated with a CCE aggregation size of 2 shown in FIG. 4.Further, as shown in FIG. 5, CCE allocating section 104 allocates threePDCCH's (of a CCE aggregation size of 4) to CCE's #12 to #15, CCE's #16to #19 and CCE's #20 to #23, to which PDCCH's of CCE aggregation sizesof 1 and 2 are not allocated, in the search space (CCE #8 to CCE #23)associated with a CCE aggregation size of 4 shown in FIG. 4. Further, asshown in FIG. 5, CCE allocating section 104 allocates one PDCCH (of aCCE aggregation size of 8) to CCE's #24 to #31, to which PDCCH's of CCEaggregation sizes of 1, 2 and 4 are not allocated, in the search space(CCE #16 to CCE #31) associated with a CCE aggregation size of 8 shownin FIG. 4.

Mobile station 200 performs demodulation, decoding and blind detectionof PDCCH's using the definition of search spaces based on the CCEaggregation sizes. By this means, it is possible to reduce the number oftimes of blind detection in demodulating section 208, decoding section209 and deciding section 210 of mobile station 200 (in FIG. 2). To bemore specific, if blind detection is performed presuming that the CCEaggregation size is 1, extracting section 207 outputs only signalsassociated with CCE #0 to CCE #9 to demodulating section 208 among CCE#0 to CCE #31 shown in FIG. 4. That is, in demodulating section 208,decoding section 209 and deciding section 210, when a CCE aggregationsize is 1, the target of blind detection is limited to the search spacesupporting CCE #0 to CCE #9. Similarly, if blind detection is performedwhen the CCE, aggregation size is 2, extracting section 207 outputs onlysignals associated with CCE #4 to CCE #15 to demodulating section 208among CCE #0 to CCE #31 shown in FIG. 4. The same applies to the casewhere the CCE aggregation size presumes 4 or 8.

Thus, each mobile station performs blind decoding using search spacesassociated with the CCE aggregation sizes. That is, by defining onesearch space information per cell, mobile stations can perform blinddecoding unless a base station notifies search space information tothese mobile stations.

Here, to reduce degradation of error rate performance of allocationinformation, the MCS of allocation information directed to mobilestations that are located near a cell edge is set lower. Therefore, thePDCCH CCE aggregation size for mobile stations that are located near acell edge increases. For example, out of the CCE aggregation sizes 1, 2,4 and 8, the CCE aggregation size for mobile stations that are locatednear a cell edge is 4 or 8.

Also, in a cell of a larger cell size, the proportion of mobile stationsrequiring transmission of allocation information with a low MCS set,that is, the proportion of mobile stations, to which PDCCH's of largerCCE aggregation size are allocated, increases. In other words, in a cellof a smaller cell size, the proportion of mobile stations that cantransmit allocation information with a high MCS set, that is, theproportion of mobile stations, to which PDCCH's of a smaller CCEaggregation size are allocated, increases.

Therefore, a base station defines search spaces that vary between cellsizes. That is, in a larger cell size, a wider search space is definedfor a larger CCE aggregation size, and a narrower search space isdefined for a smaller CCE aggregation size. Also, in a smaller cellsize, a narrower search space is defined for a larger CCE aggregationsize, and a wider search space is defined for a smaller CCE aggregationsize.

Also, CCE allocating section 104 allocates control information to aspecific search space among a plurality of search spaces defined percell.

For example, FIG. 6 shows an example of search space information in acell of a larger cell size than a cell in which the search spaceinformation shown in FIG. 3 is set. To be more specific, the searchspace associated with a CCE aggregation size of 1 is defined where theCCE number representing the starting location is CCE #0 and the numberof CCE's is 6. Similarly, the search space associated with a CCEaggregation size of 2 is defined where the CCE number representing thestarting location is CCE #2 and the number of CCE's is 8. The sameapplies to the case where the CCE aggregation size is 4 or 8.

That is, as shown in FIG. 7, CCE allocating section 104 can allocatemaximum six PDCCH's of a CCE aggregation size of 1 to the search spaceof CCE #0 to CCE #5. Similarly, CCE allocating section 104 can allocatemaximum four PDCCH's of a CCE aggregation size of 2 to the search spaceof CCE #2 to CCE #9, allocate maximum live PDCCH's of a CCE aggregationsize of 4 to the search space of CCE #4 to CCE #23, and allocate maximumthree PDCCH's of a CCE aggregation size of 8 to the search space of CCE#8 to CCE #31.

Here, if the search spaces shown in FIG. 7 are compared to the searchspaces shown in FIG. 4, in a smaller CCE aggregation size, that is, in aCCE aggregation size of 1 (or a CCE aggregation size of 2), the numberof PDCCH's allocated decreases from 10 (6) to 6 (4). By contrast, in alarger CCE aggregation size, that is, in a CCE aggregation size of 4 (ora CCE aggregation size of 8), the number of PDCCH's allocated increasesform 4 (2) to 5 (3). That is, in CCE allocating section 104, the numberof PDCCH's of a larger CCE aggregation size increases in a larger cellsize, so that it is possible to allocate more PDCCH's of a larger CCEaggregation size. In other words, in CCE allocating section 104, thenumber of PDCCH's of a smaller CCE aggregation size increases in asmaller cell size, so that it is possible to allocate more PDCCH's of asmaller CCE aggregation size.

Thus, according to the present embodiment, only search spaces that aredefined per cell are the target of blind decoding in a mobile station,so that it is possible to reduce the number of times to perform blinddecoding. Also, mobile stations specify search spaces based on searchspace information broadcasted for all the mobile stations from a basestation, so that new notification information per mobile station is notrequired. Therefore, according to the present embodiment, it is possibleto reduce the number of times of blind decoding, without increasing theoverhead due to notification information.

Further, according to the present embodiment, PDCCH's are allocated to asearch space associated with the CCE aggregation size. By this means, ina plurality of CCE's, the CCE aggregation size of PDCCH's for use islimited. Therefore, according to the present embodiment, by associatingPUCCH's with only CCE's of the minimum numbers among the CCE's formingPDCCH's for use, it is possible to reduce the amount of resourcesreserved for PUCCH's.

Also, a case has been described above with the present embodiment wherePDCCH's of all CCE aggregation sizes can be transmitted to a certainmobile station. However, with the present invention, it is equallypossible to determine the CCE aggregation size per mobile station. Forexample, for a mobile station that is located near a cell edge, channelquality is poor, and, consequently, the ratio of transmission with alower MCS increases. Therefore, the CCE aggregation size in a mobilestation that is located near a cell edge is limited to 4 or 8. Also, fora mobile station that is located near a cell center, channel quality isgood, and, consequently, the ratio of transmission with a higher MCSincreases. Therefore, the CCE aggregation size of a mobile station thatis located near a cell center is limited to 1 or 2. By this means, it iseasier to further specify a search space, so that it is possible tofurther reduce the number of times a mobile station performs blinddecoding.

Also, although a case has been described above with the presentembodiment where the definition of search spaces is set based on thecell size, with the present invention, it is equally possible to set thedefinition of search spaces based on, for example, the bias ofdistribution of mobile stations in a cell.

Embodiment 2

In the search spaces shown in FIG. 4 of Embodiment 1, if an odd numberof PDCCH's of a given CCE aggregation size are used, a CCE may arisewhich cannot be used as a PDCCH of a larger CCE aggregation size thanthe given CCE aggregation size.

For example, in the search spaces shown in FIG. 4, if five PDCCH's of aCCE aggregation size of 1 are used. CCE #0 to CCE #4 are occupied. Inthis case, out of PDCCH's of a CCE aggregation size of 2, the PDCCHformed with CCE #4 and CCE #5 cannot be used because CCE #4 is alreadyused. That is, CCE #5 is not used. Similarly, for example, if threePDCCH's of a CCE aggregation size of 4 are used, CCE #8 to CCE #19 areoccupied. In this case, out of PDCCH's of a CCE aggregation size of 8,the PDCCH formed with CCE #16 to CCE #23 cannot be used because CCE #16to CCE #19 are already used. That is, CCE #20 to CCE #23 are not used.Thus, a part of CCE's forming a PDCCH is used by another PDCCH of adifferent CCE aggregation size, and, consequently, the use efficiency ofCCE's becomes poor.

Therefore, according to the present embodiment, allocation informationis allocated to a specific search space formed with CCE's of lower CCEnumbers in a larger CCE aggregation size.

To be more specific, as shown in FIG. 8, a search space formed withsixteen CCE's from CCE #0 to CCE #15 is defined when the CCE aggregationsize is 8, a search space formed with sixteen CCE's from CCE #8 to CCE#23 is defined when the CCE aggregation size is 4, a search space formedwith twelve CCE's from CCE #16 to CCE #27 is defined when the CCEaggregation size is 2, and a search space formed with ten CCE's from CCE#22 to CCE #31 is defined when the CCE aggregation size is 1.

Here, a case will be explained where CCE allocating section 104 of basestation 100 allocates five PDCCH's of a CCE aggregation size of 1, threePDCCH's of a CCE aggregation size of 2, two PDCCH's of a CCE aggregationsize of 4 and one PDCCH of a CCE aggregation size of 8.

First, as shown in FIG. 8, CCE allocating section 104 allocates onePDCCH (of a CCE aggregation size of 8) to CCE #0 to CCE #7 in the searchspace (CCE #0 to CCE #15) associated with a CCE aggregation size of 8.Next, as shown in FIG. 8, CCE allocating section 104 allocates twoPDCCH's (of a CCE aggregation size of 4) to CCE's #8 to #11 and CCE's#12 to #15, to which a PDCCH of a CCE aggregation size of 8 is notallocated, in the search space (CCE #8 to CCE #23) associated with a CCEaggregation size of 4. Further, as shown in FIG. 8, CCE allocatingsection 104 allocates three PDCCH's (of a CCE aggregation size of 2) toCCE's #16 and #17. CCE's #18 and #19 and CCE's #20 and #21, to whichPDCCH's of CCE aggregation sizes of 8 and 4 are not allocated, in thesearch space (CCE #16 to CCE #27) associated with a CCE aggregation sizeof 2. Further, as shown in FIG. 8, CCE allocating section 104 allocatesfive PDCCH's (of a CCE aggregation size of 1) to CCE's #22 to #26 in thesearch space (CCE #16 to CCE #31) associated with a CCE aggregation sizeof 1. Also, different CCE's from the CCE's used for PDCCH's, that is,unused CCE's are concentrated in CCE numbers (i.e. CCE #27 to CCE #31)near the tail end among CCE #0 to CCE #31.

That is, in CCE allocating section 104, if a plurality of PDCCH's ofdifferent CCE aggregation sizes are allocated, it is possible toallocate a plurality of PDCCH's to a plurality of consecutive CCE'swithout causing unused CCE's. By this means, in each CCE, CCE's are usedin order from the CCE of the lowest CCE number, and, if unused CCE'soccur, these unused CCE's are likely to be concentrated in CCE numbersnear the tail end.

Thus, if CCE's of lower CCE numbers are used in order from PDCCH's ofthe largest CCE aggregation size, CCE allocating section 104 canallocate PDCCH's of a different CCE aggregation size in order from theCCE immediately after the CCE's to which PDCCH's of a larger CCEaggregation size are allocated. Therefore, unlike Embodiment 1, it ispossible to prevent CCE's from being unavailable because PDCCH's of adifferent CCE aggregation size are already allocated to these CCE's, sothat it is possible to allocate PDCCH's efficiently. Also, unused CCE'sare concentrated in CCE numbers near the tail end, and, consequently,for example, a base station reduces and transmits the number of CCE's towhich PDCCH's are actually allocated (in the above example, CCE's arereduced to 27) and which are transmitted, so that it is possible to useavailable resources (in the above example, five CCE's from CCE #27 toCCE #31) efficiently as data resources. Also, even if unused CCE's arepresent in locations other than the locations of CCE numbers near thetail end, although a base station can reduce the number of CCE's towhich PDCCH's are allocated and which are transmitted, an enormousamount of control information is necessary to notify which CCE isunused. However, as in the present embodiment, when unused CCE's areconcentrated in CCE numbers near the tail end, only the number of CCE'sfor transmission needs to be notified, so that only a small amount ofcontrol information is required.

Thus, according to the present embodiment, allocation information isallocated to a specific search space formed with CCE's of lower CCEnumbers in a larger CCE aggregation size. By this means, it is possibleto allocate PDCCH's in order from the CCE of the lowest CCE numberwithout causing unused CCE's, and gather unused CCE's in consecutiveCCE's of CCE numbers near the tail end. Therefore, according to thepresent embodiment, it is possible to allocate PDCCH's to CCE's moreefficiently than in Embodiment 1 and use unused CCE's efficiently asdata resources.

Embodiment 3

A case will be explained with the present embodiment where downlinkallocation information and uplink allocation information share aplurality of CCE's.

The method of allocating CCE's in the present embodiment will beexplained.

<Allocating Method 1>

With the present embodiment, in a plurality of CCE's forming a specificsearch space, downlink allocation information for notifying a downlinkallocation result is allocated in ascending order from the CCE of thelowest CCE number, and uplink allocation information for notifying anuplink allocation result is allocated in descending order from the CCEof the highest CCE number.

This will be explained below in detail. Here, the same search spaces asthose in FIG. 8 of Embodiment 2 will be used. Also, the above will beexplained focusing on the case where the CCE aggregation size is 1.

As shown in FIG. 9, in the search space (CCE's #22 to #31) matching aCCE aggregation size of 1, CCE allocating section 104 allocates downlinkallocation information (of a CCE aggregation size of 1) in ascendingorder from CCE #22, which is the CCE of the lowest CCE number. That is,CCE allocating section 104 allocates downlink allocation information inorder from CCE #22 to CC #31. By contrast, as shown in FIG. 9, in thesearch space (CCE's #22 to #31) matching a CCE aggregation size of 1,CCE allocating section 104 allocates uplink allocation information (of aCCE aggregation size of 1) in descending order from CCE #31, which isthe CCE of the highest CCE number. That is, CCE allocating section 104allocates downlink allocation information in order from CCE #31 to CCE#22. The same applies to CCE aggregation sizes of 2, 4 and 8.

In CCE #22 to CCE #31 shown in FIG. 9, CCE #22 is used most frequentlyas a PDCCH for downlink allocation information, and CCE #31 is used mostfrequently as a PDCCH for uplink allocation information. In other words,CCE #22 is used least frequently as a PDCCH for uplink allocationinformation. That is, in CCE #22 to CCE #31 shown in FIG. 9, CCE #22,which is used least frequently as a PDCCH for uplink allocationinformation, is used as a PDCCH for downlink allocation, and CCE #31,which is used least frequently as a PDCCH for downlink allocationinformation, is used as a PDCCH for uplink allocation information.

Thus, with the present allocating method, even if downlink allocationinformation and uplink allocation information share a plurality ofCCE's, it is possible to acquire the same effect as in Embodiment 2 anduse the plurality of CCE's efficiently between downlink allocationinformation and uplink allocation information.

Further, a plurality of items of downlink allocation information or aplurality of items of uplink allocation information are not transmittedto a mobile station. Consequently, when a mobile station decidesdownlink allocation information, by performing blind detection in orderfrom the CCE of the lowest CCE number and stopping blind detection ofdownlink allocation information at the time the PDCCH for that mobilestation is found, it is possible to reduce an average number of times ofblind detection, compared to a case where uplink allocation informationand downlink allocation information are mapped in a random manner.Therefore, according to the present embodiment, it is possible to reducethe power consumption in mobile stations.

<Allocating Method 2>

With the present allocating method, allocation information is allocatedto a search space which is formed symmetrically with CCE's of lower CCEnumbers and CCE's of higher CCE numbers in the case of a larger CCEaggregation size.

This will be explained below in detail. As shown in FIG. 10, searchspaces formed with eight CCE's from CCE #0 to CCE #7 and eight CCE'sfrom CCE #24 to CCE #31 are defined when the CCE aggregation size is 8,search spaces formed with eight CCE's from CCE #4 to CCE #11 and eightCCE's from CCE #20 to CCE #27 are defined when the CCE aggregation sizeis 4, search spaces formed with six CCE's from CCE #8 to CCE #13 and sixCCE's from CCE #18 to CCE #23 are defined when the CCE aggregation sizeis 2, and a search space formed with eight CCE's from CCE #12 to CCE #19is defined when the CCE aggregation size is 1.

That is, each search space is formed with CCE's symmetrically withreference to the center of CCE #0 to CCE #31 (i.e. between CCE #15 andCCE #16).

Also, as shown in FIG. 10, in the same way as in allocating method 1,CCE allocating section 104 allocates downlink allocation information inascending order from the CCE of the lowest CCE number in each searchspace, and allocates uplink allocation information in descending orderfrom the CCE of the highest CCE number in each search space. That is, inCCE #0 to CCE #31 shown in FIG. 10, while the search space (CCE #0 toCCE #15) formed with CCE's of lower CCE numbers than the center of allCCE's is used more frequently as PDCCH's for downlink allocationinformation, the search space (CCE #16 to CCE #31) formed with CCE's ofhigher CCE numbers than the center of all CCE's is used more frequentlyas PDCCH's for uplink allocation information.

Thus, according to the present allocating method, compared to allocatingmethod 1, it is possible to allocate downlink allocation information anduplink allocation information of different CCE aggregation sizesseparately, so that it is possible to perform scheduling more easily tooptimize allocation of CCE's for downlink allocation information andCCE's for uplink allocation information.

The methods of allocating CCE's have been described above.

Thus, according to the present embodiment, even if downlink allocationinformation and uplink allocation information share a plurality ofCCE's, it is possible to reduce the number of times of blind decodingwithout increasing the overhead due to notification information.

Also, according to the present embodiment, it is possible to acquire thesame effect as above by allocating uplink allocation information inascending order from the CCE of the lowest CCE number and allocatingdownlink allocation information in descending order from the CCE of thehighest CCE number among a plurality of CCE's forming a specific searchspace.

Embodiment 4

With the present embodiment, the allocation information is allocated toa specific search space shifted based on the CFI (Control FormatIndicator) value.

CFI, which is information indicating the amount of PDCCH resources, isnotified from a base station to mobile stations. To be more specific,the CFI value (=3, 2, 1) is associated with the number of OFDM symbolsincluding allocation information. Here, while the above search spaceinformation is broadcasted semi-statically from the base station to themobile stations, CFI is notified dynamically from the base station tothe mobile stations on a per subframe basis. That is, OFDM symbolsincluding allocation information vary between subframes dynamically.Consequently, if the definition of search spaces is set based on thenumber of OFDM symbols including allocation information, that is, basedon the total number of CCE's, it is necessary to notify search spaceinformation from the base station to the mobile stations every time CFIvaries, and therefore the overhead due to notification informationincreases.

Therefore, with the present embodiment, allocation information isallocated to a specific search space shifted based on the CFI value.This will be explained below in detail. Here, as shown in FIG. 11, thesearch space used in the case of CFI=3 is the same as the search spaceshown in FIG. 8 of Embodiment 2. In this case, as shown in FIG. 11, thetotal number of CCE's N_(CCE)(3)=32 holds. Also, assume that thestarting location of the search space is n_(CCE4)(3)=8 in the case wherethe CCE aggregation size is 4, the starting location of the search spaceis n_(CCE2)(3)=16 in the case where the CCE aggregation size is 2 andthe starting location of the search space is n_(CCE1)(3)=22 in the casewhere the CCE aggregation size is 1, and these values are broadcasted inadvance from a base station to mobile stations.

CCE allocating section 104 calculates the search space in CFI=i (i=1, 2,3) and changes the definition of the search space based on the followingequations.

n _(CCE4)(i)=n _(CCE4)(3)−N _(CCE)(3)+N _(CCE)(i)

n _(CCE2)(i)=n _(CCE2)(3)−N _(CCE)(3)+N _(CCE)(i)

n _(CCE1)(i)=n _(CCE1)(3)−N _(CCE)(3)+N _(CCE)(i)

Here, if the calculation result is negative, the starting location ofthat search space is CCE #0. In the right member of the above equations,the second term and the third term represent the difference between thetotal number of CCE's in the subframe of CFI=3 and the total number ofCCE's in the subframe of CFI=i. That is, the starting location of thesearch space matching each CCE aggregation size in the case of CFI=i isshifted forward by the difference of the total number of CCE's from thestarting location of the search space matching each aggregation size inthe case of CFI=3.

For example, in the case of the sub frame of CFI=2, the total number ofCCE's N_(CCE)(2)=24 holds, and therefore CCE allocating section 104defines search spaces based on the above equations. To be more specific,the starting location of the search space matching each CCE aggregationsize is calculated as follows.

n _(CCE4)(2)=n _(CCE4)(3)−N _(CCE)(3)+N _(CCE)(2)=0

n _(CCE2)(2)=n _(CCE2)(3)−N _(CCE)(3)+N _(CCE)(2)=8

n _(CCE1)(2)=n _(CCE1)(3)−N _(CCE)(3)+N _(CCE)(2)=14

Therefore, CCE allocating section 104 defines the search spaces shown inFIG. 12. That is, the search space matching each CCE aggregation size inthe case of CFI=2 is acquired by shifting the CCE numbers by eightCCE's, which are the difference between the total number of CCE's in thecase of CFI=3 (N_(CCE)(3)=32) and the total number of CCE's in the caseof CFI=2 (N_(CCE)(2)=24). That is, in CCE allocating section 104, thesearch spaces are shifted based on the CFI value. Similarly, bycalculating the CCE number corresponding to the starting location of thesearch space matching each aggregation size in the case of CFI=1 (i.e.the total number of CCE's N_(CCE)(1)=14), CCE allocating section 104 canacquire the search spaces shown in FIG. 13. Here, in FIG. 13, uponcalculating the starting locations n_(CCE4)(1) and n_(CCE2)(1) of thesearch spaces matching the cases of CCE aggregation sizes of 4 and 2,the calculation results are negative, and therefore the startinglocations are n_(CCE4)(1)=n_(CCE2)(1)=0.

Also, in the same way as in CCE allocating section 104, deciding section210 (in FIG. 2) of mobile station 200 performs blind detection of onlythe allocation information allocated to a specific search space shiftedbased on the CFI value notified from base station 100, for decidingwhether or not that allocation information is the allocation informationdirected to that mobile station. That is, even if CFI varies, it ispossible to find a common definition of search spaces between CCEallocating section 104 of base station 100 and deciding section 210 ofmobile station 200.

Thus, according to the present embodiment, even if the CFI value varies,mobile stations can change the definition of search spaces using thedefinition of search spaces broadcasted from a base station to themobile stations. By this means, it is possible to form optimal searchspaces based on the CFI value without increasing the overhead due tofurther notification information. Therefore, according to the presentembodiment, even if CFI varies, it is possible to acquire the sameeffect as in Embodiment 1.

Embodiment 5

A case will be explained with the present embodiment where CCE's andPUCCH's are associated.

Upon associating CCE's and PUCCH's, a mobile station decides a PUCCHassociated with the lowest CCE number among one or a plurality of CCE'sforming the PDCCH to which allocation information for that mobilestation is mapped, as the PUCCH for that mobile station. Therefore, ifall CCE's are associated with PUCCH's on a one-to-one basis, a PUCCHthat is not actually used is found upon CCE aggregation, and,consequently, resource use efficiency degrades. For example, if CCE #0to CCE #3 are the CCE's associated with physical resources to whichallocation information for the subject mobile station is mapped, themobile station decides PUCCH #0 associated with CCE #0 of the lowestnumber among CCE #0 to CCE #3, as the PUCCH for that mobile station.That is, three PUCCH's from PUCCH #1 to PUCCH #3 other than the PUCCHfor the subject mobile station are not used and are wasted.

Therefore, for example, if the search spaces shown in FIG. 11 ofEmbodiment 4 are defined, with respect to a plurality of CCE's formingthe PDCCH belonging to each search space, a mobile station associatesone PUCCH with the number of CCE's matching the CCE aggregation size.For example, one PUCCH is associated with eight CCE's with respect to aplurality of CCE's forming a PDCCH of a CCE aggregation size of 8, andone PUCCH is associated with four CCE's with respect to a plurality ofCCE's forming a PDCCH of a CCE aggregation size of 4. That is, withrespect to a plurality of CCE's forming a PDCCH of a CCE aggregationsize of n, one PUCCH is associated with n CCE's.

However, as described in Embodiment 4, if the CFI value varies persubframe, the range of the search space matching each CCE aggregationsize is shifted. By this means, the CCE's forming the PDCCH of each CCEaggregation size vary based on the CFI value, and therefore PUCCH'sassociated with the CCE's forming the PDCCH of each CCE aggregation sizevary. That is, if the CFI value varies, the association between CCE'sand PUCCH's is not optimum.

Also, if the association between CCE's and PUCCH resources is notifiedfrom a base station to a mobile station every time the CFI value varies,the overhead due to notification information increases.

Therefore, based on the association between CCE's in which downlinkallocation information is included and specific PUCCH resources to whicha response signal to downlink data is allocated, where the associationvaries based on the CFI value, the present embodiment controlsblock-wise spreading code sequences and the cyclic shift values of ZACsequences for that response signal.

Among a plurality of PUCCH's, deciding section 210 of mobile station 200(in FIG. 2) according to the present embodiment decides a specific PUCCHto which a response signal to downlink data is allocated, based on CCE'sthat are occupied by PDCCH's allocated to a specific search spacematching the CCE aggregation size of the PDCCH to which allocationinformation for that mobile station is allocated, among a plurality ofsearch spaces that vary depending on the CFI value as in Embodiment 4.

Control section 211 controls block-wise spreading code sequences and thecyclic shift values of ZAC sequences for a response signal, based on theassociation between the specific PUCCH decided in deciding section 210,the cyclic shift value of the ZAC sequence and the block-wise spreadingcode sequence, where the association varies depending on the CFI value.

This will be explained in detail. The present embodiment uses the samesearch spaces as in FIG. 11 (CFI=3), FIG. 12 (CFI=2) and FIG. 13 (CFI=3)in Embodiment 4. Also, as in Embodiment 4, base station 100 broadcastssearch space information (n_(CCE4)(3)=8, n_(CCE2)(3)=16, n_(CCE1)(3)=22)to mobile station 200.

Among a plurality of PUCCH's, control section 211 reserves a PUCCHresource associated with the lowest CCE number occupied by a PDCCH ofthe smallest CCE aggregation size.

First, the case of CFI=3 will be explained. Among CCE #0 to CCE #31(CFI=3) shown in FIG. 11, in CCE #0 to CCE #7 immediately before thestarting location n_(CCE4)(3)=8 (CCE #8) of the search space matchingthe case of a CCE aggregation size of 4, one PUCCH resource isassociated with CCE #0 of the lowest number among the CCE's formingPDCCH's.

Next, as shown in FIG. 11, in CCE #8 to CCE #15 between the startinglocation n_(CCE4)(3)=8 (CCE #8) of the search space matching the case ofa CCE aggregation size of 4 and the starting location n_(CCE2)(3)=16(CCE #16) of the search space matching the case of a CCE aggregationsize of 2, two PUCCH resources are associated with the CCE's of thelowest numbers CCE #8 and CCE #12 forming two PDCCH's of a CCEaggregation size of 4 that is the smallest CCE aggregation size.

Similarly, as shown in FIG. 11, in CCE #16 to CCE #21 between thestarting location n_(CCE2)(3)=16 (CCE #16) of the search space matchingthe case of a CCE aggregation size of 2 and the starting locationn_(CCE1)(3)=22 (CCE #22) of the search space matching the case of a CCEaggregation size of 1, three PUCCH resources are associated with theCCE's of the lowest numbers CCE #16, CCE #18 and CCE #20 forming threePDCCH's of a CCE aggregation size of 2 that is the smallest CCEaggregation size.

Similarly, as shown in FIG. 11, in CCE #22 to CCE #31 greater than thestarting location n_(CCE1)(3)=22 (CCE #22) of the search space matchingthe case of a CCE aggregation size of 1, ten PUCCH resources areassociated with CCE #22 to CCE #31 forming ten PDCCH's of a CCEaggregation size of 1.

That is, in the field below the starting location n_(CCE4)(i) of thefield corresponding to the CCE's of CFI=i, one PUCCH resource isassociated with eight CCE's. Also, in the field equal to or above thestarting location n_(CCE4)(i) and below the starting locationn_(CCE2)(i), one PUCCH resource is associated with four CCE's.Similarly, in the field equal to or above the starting locationn_(CCE2)(i) and below the starting location n_(CCE1)(i), one PUCCHresource is associated with two CCE's. Also, in the field above thestarting location n_(CCE1)(i), one PUCCH resource is associated with oneCCE.

Thus, based on search space information broadcasted from base station100, control section 211 controls PUCCH resources for a response signalaccording to the association between CCE's and PUCCH resources, wherethe association varies depending on the CFI value.

Here, as shown in FIG. 14, assume that the priority order regarding ause of physical resources associated with PUCCH's (i.e. the use order ofsequence numbers) is notified in advance from a base station to a mobilestation. Here, a physical resource (i.e. PUCCH resource) of a lowerPUCCH number is preferentially associated with a CCE. In the associationshown in FIG. 14, PUCCH numbers are defined by the cyclic shift values(0 to 11) of ZAC sequences and the sequence numbers (0 to 2) ofblock-wise spreading code sequences. In this case, PUCCH resourcesassociated with CCE's are as shown in FIG. 15. To be more specific, asshown in FIG. 15, the PUCCH number associated with CCE #0 is defined byZAC sequence #0 and block wise spreading code sequence #0, and the PUCCHnumber associated with CCE #8 is defined by ZAC sequence #0 andblock-wise spreading code sequence #2. Also, the present invention isnot limited to these sequence lengths.

Next, the association between CCE's and PUCCH resources in CFI=2 will beexplained.

In the same way as in CFI=3, control section 211 associates a PUCCHresource and the CCE lowest number occupied by the PDCCH of the smallestCCE aggregation size in the search space of CFI=2 among a plurality ofPUCCH's.

That is, in the case of CFI=2, as shown in FIG. 12, PUCCH resources areassociated with the CCE's of the lowest numbers CCE #0 and CCE #4forming the PDCCH's of a CCE aggregation size of 4 among CCE #0 to CCE#7, PUCCH resources are associated with the CCE's of the lowest numbersCCE #8, CCE #10 and CCE #12 forming the PDCCH's of a CCE aggregationsize of 2 among CCE #8 to CCE #13, and PUCCH resources are associatedwith CCE #14 to CCE #23 forming PDCCH's of a CCE aggregation size of 1among CCE #14 to CCE #23.

In this case, PUCCH resources associated with CCE numbers are as shownin FIG. 16. Here, comparing associated PUCCH resources in CFI=3 (in FIG.15) and associated PUCCH resources in CFI=2 (in FIG. 16), the associatedPUCCH resources in CFI=2 shown in FIG. 16 are reduced. Further, theassociated CCE numbers are different between the PUCCH resources shownin FIG. 15 and the PUCCH resources shown in FIG. 16.

Thus, according to the present embodiment, even if the CFI value varies,by using search space information broadcasted from a base station, amobile station can associate CCE's and PUCCH's based on search spacesthat vary depending on the CFI value. Further, even if the CFI valuevaries, by reserving only the minimum PUCCH resources, it is possible toprepare sufficient resources for transmitting response signals.

Also, in the same way as in the case of CFI=1, as shown in FIG. 17,control section 211 updates the association between CCE's and PUCCH's.

Thus, according to the present embodiment, based on search spaceinformation (about the starling location of the search space matchingeach CCE aggregation size) in the specific CFI value, a mobile stationcan associate CCE's and PUCCH resources according to the change of theCFI value. Therefore, according to the present embodiment, even if theCFI value varies, by optimally associating CCE's and PUCCH resourcesaccording to the definition of search spaces that varies depending onCFI and reserving only the minimum PUCCH resources, it is possible toprepare sufficient resources for transmitting response signals withoutnotifying, from a base station to mobile stations, the associationbetween CCE's and PUCCH resources every time the CFI value varies.

Also, although a case has been described above with the presentembodiment where PUCCH resources are defined based on the associationbetween ZAC sequences and block-wise spreading code sequence shown inFIG. 15, FIG. 16 and FIG. 17, the present invention is not limited tothe association between ZAC sequences and block-wise spreading codesequence shown in FIG. 15, FIG. 16 and FIG. 17.

Also, as PUCCH resources, it is possible to use resources other than thecyclic shift values of ZAC sequences and block-wise spreading codesequences. For example, resources that are separated by frequencies suchas subcarriers and resources that are separated by time such as SC-FDMAsymbols are possible.

Embodiments of the present invention have been described above.

Also, the total number of CCE's that can be used per subframe (i.e. thetotal number of CCE's that can be present in one subframe) in the aboveembodiments varies depending on the system bandwidth, the number of OFDMsymbols that can be used as CCE's, and the total number of controlsignals (e.g. ACK/NACK to uplink data) that are not used to notifyresource allocation results of downlink/uplink data.

Also, a PUCCH used for explanation in the above embodiments is thechannel for feeding back an ACK or NACK, and therefore may be referredto as an “ACK/NACK channel.”

Also, although cases have been described above with embodiments whereCCE's and PUCCH's (i.e. response signals to downlink data) areassociated, the present invention can acquire the same effect as aboveby associating CCE's and PHICH's (Physical Hybrid ARQ IndicatorCHannels). Here, response signals to uplink data are allocated to thePHICH's.

Also, even in the ease of using the search spaces shown in FIG. 18, itis possible to implement the present invention in the same way as above.FIG. 18 shows grouping a plurality of mobile stations and using thesearch spaces that are used per group and the search spaces that areused per CCE aggregation size. Thus, even in the case of distributing aplurality of CCE's to a plurality of mobile station groups and applyingthe present invention to each group, it is possible to acquire the sameeffect as above. Also, even in the case of using the definition ofsearch spaces shown in FIG. 19, it is possible to implement the presentinvention in the same way as above. As shown in FIG. 19, a configurationis employed where the search spaces matching respective CCE aggregationsizes do not overlap. By this means, different search spaces do notoverlap, so that it is possible to acquire the same effect as above andreduce the resources to reserve for PUCCH resources.

Also, even in the case of feeding back control information other thanresponse signals, it is possible to implement the present invention inthe same way as above.

Also, a mobile station may be referred to as a “terminal station.” “UE,”“MT,” “MS” or “STA (STAtion)”. Also, a base station may be referred toas “Node B,” “BS” or “AP.” Also, a subcarrier may be referred to as a“tone.” Also, a CP may be referred to as a “GI (Guard Interval)”. Also,a CCE number may be referred to as a “CCE index.”

Also, the error detecting method is not limited to CRC check.

Also, a method of performing conversion between the frequency domain andthe time domain is not limited to IFFT and FFT.

Also, although a case has been described above with the embodimentswhere signals are transmitted using OFDM as a downlink transmissionscheme and SC-FDMA as an uplink transmission scheme, the presentinvention is equally applicable to the case where transmission schemesother than OFDM and SC-F DMA are used.

Although a case has been described with the above embodiments as anexample where the present invention is implemented with hardware, thepresent invention can be implemented with software.

Furthermore, each function block employed in the description of each ofthe aforementioned embodiments may typically be implemented as an LSIconstituted by an integrated circuit. These may be individual chips orpartially or totally contained on a single chip. “LSI” is adopted herebut this may also be referred to as “IC,” “system LSI,” “super LSI,” or“ultra LSI” depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSI's, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of an FPGA (FieldProgrammable Gate Array) or a reconfigurable processor where connectionsand settings of circuit cells in an LSI can be reconfigured is alsopossible.

Further, if integrated circuit technology comes out to replace LSI's asa result of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application o biotechnology isalso possible.

The disclosure of Japanese Patent Application No. 2007-280921, filed onOct. 29, 2007, including the specification, drawings and abstract, isincorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The present invention is applicable to, for example, mobilecommunication systems.

1. A terminal apparatus comprising: a decoding section configured todecode a downlink control channel, which is transmitted on one or morecontrol channel element(s) (CCE(s)) with consecutive CCE number(s) froma base station, in a search space that is comprised of a plurality ofCCEs; and a transmitting section configured to transmit a responsesignal to the base station on a uplink control channel, an index ofwhich is associated with a CCE number of the CCE, on which the downlinkcontrol channel is transmitted, wherein: the search space is comprisedof the plurality of CCEs corresponding to a plurality of downlinkcontrol channel candidates to be attempted to be decoded; and the searchspace for each aggregation size corresponding to a number of the CCE(s),on which the downlink control channel is transmitted, is comprised ofthe plurality of CCEs that are defined by starting on a CCE with a CCEnumber, which depends on both a total number of CCEs in a subframe andthe aggregation size, and at least part of the search space for the eachaggregation size is comprised of CCEs with consecutive CCE numbers. 2.The terminal apparatus according to claim 1, further comprising: areceiving section configured to receive the downlink control channel,which is transmitted on said one or more CCE(s) from the base station.3. The terminal apparatus according to claim 1, further comprising: aspreading section configured to spread the response signal with asequence determined from the index of the uplink control channel,wherein said transmitting section transmits the spread response signal.4. The terminal apparatus according to claim 1, wherein the CCE with theCCE number is specific to both the total number of CCEs in a subframeand the aggregation size.
 5. The terminal apparatus according to claim1, wherein the search space comprises a specific number of CCEsaccording to the aggregation size.
 6. The terminal apparatus accordingto claim 1, wherein the CCE number is different between at least two ofthe aggregation sizes.
 7. The terminal apparatus according to claim 1,wherein a minimum CCE number of the CCEs, of which the search space iscomprised, depends on both the total number of CCEs in a subframe andthe aggregation size.
 8. The terminal apparatus according to claim 1,wherein the search space for the each aggregation size is comprised ofthe CCEs with CCE numbers, which depend on both the total number of CCEsin a subframe and the aggregation size.
 9. The terminal apparatusaccording to claim 1, wherein each of the search spaces for at least twoof the aggregation sizes includes a CCE different from a CCE included inthe other of the search spaces.
 10. The terminal apparatus according toclaim 1, wherein the search spaces for at least two of the aggregationsizes do not overlap in at least part of each of the search spaces. 11.The terminal apparatus according to claim further comprising: areceiving section configured to receive a control format indicator(CFI), which indicates a number of symbols used for control channels ina subframe, and the total number of CCEs in the sub frame is obtainedbased on the CFI.
 12. The terminal apparatus according to claim 1,wherein the total number of CCEs depends on a system bandwidth, a numberof symbols used for control channels and a number of ACK/NACK channelsfor uplink data.
 13. The terminal apparatus according to claim 1,wherein the total number of CCEs is larger than a maximum number of theaggregation size.
 14. A method for transmitting a response signal at aterminal comprising: decoding a downlink control channel, which istransmitted on one or more control channel element(s) (CCE(s)) withconsecutive CCE number(s) from a base station, in a search space that iscomprised of a plurality of CCEs; and transmitting the response signalto the base station on a uplink control channel, an index of which isassociated with a CCE number of the CCE, on which the downlink controlchannel is transmitted, wherein: the search space is comprised of theplurality of CCEs corresponding to a plurality of downlink controlchannel candidates to be attempted to be decoded; and the search spacefor each aggregation size corresponding to a number of the CCE(s), onwhich the downlink control channel is transmitted, is comprised of theplurality of CCEs that are defined by starting on a CCE with a CCEnumber, which depends on both a total number of CCEs in a subframe andthe aggregation size, and at least part of the search space for the eachaggregation size is comprised of CCEs with consecutive CCE numbers. 15.The method according to claim 14, wherein the CCE number is differentbetween at least two of the aggregation sizes.
 16. The method accordingto claim 14, wherein the search space for the each aggregation size iscomprised of the CCEs with CCE numbers, which depend on both the totalnumber of CCEs in a sub frame and the aggregation size.
 17. The methodaccording to claim 14, wherein each of the search spaces for at leasttwo of the aggregation sizes includes a CCE different from a CCEincluded in the other of the search spaces.
 18. The method according toclaim 14, wherein the search spaces for at least two of the aggregationsizes do not overlap in at least part of each of the search spaces. 19.The method according to claim 14, wherein the total number of CCEsdepends on a system bandwidth, a number of symbols used for controlchannels and a number of ACK/NACK channels for uplink data.
 20. Themethod according to claim 14, wherein the total number of CCEs is largerthan a maximum number of the aggregation size.